github.com/jandre/docker@v1.7.0/pkg/stringid/stringid.go (about)

     1  package stringid
     2  
     3  import (
     4  	"crypto/rand"
     5  	"encoding/hex"
     6  	"io"
     7  	"regexp"
     8  	"strconv"
     9  )
    10  
    11  const shortLen = 12
    12  
    13  var validShortID = regexp.MustCompile("^[a-z0-9]{12}$")
    14  
    15  // Determine if an arbitrary string *looks like* a short ID.
    16  func IsShortID(id string) bool {
    17  	return validShortID.MatchString(id)
    18  }
    19  
    20  // TruncateID returns a shorthand version of a string identifier for convenience.
    21  // A collision with other shorthands is very unlikely, but possible.
    22  // In case of a collision a lookup with TruncIndex.Get() will fail, and the caller
    23  // will need to use a langer prefix, or the full-length Id.
    24  func TruncateID(id string) string {
    25  	trimTo := shortLen
    26  	if len(id) < shortLen {
    27  		trimTo = len(id)
    28  	}
    29  	return id[:trimTo]
    30  }
    31  
    32  // GenerateRandomID returns an unique id
    33  func GenerateRandomID() string {
    34  	for {
    35  		id := make([]byte, 32)
    36  		if _, err := io.ReadFull(rand.Reader, id); err != nil {
    37  			panic(err) // This shouldn't happen
    38  		}
    39  		value := hex.EncodeToString(id)
    40  		// if we try to parse the truncated for as an int and we don't have
    41  		// an error then the value is all numberic and causes issues when
    42  		// used as a hostname. ref #3869
    43  		if _, err := strconv.ParseInt(TruncateID(value), 10, 64); err == nil {
    44  			continue
    45  		}
    46  		return value
    47  	}
    48  }